Book/Report

FZJ-2019-01352

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Korrelation von Magnetismus, Struktur und Morphologie ultradünner Eisen- und Manganfilme auf einkristallinen Metallsubstraten

Feldmann, B. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21590

Report No.: Juel-3185

Abstract: Ultrathin Fe and Mn films were deposited on single crystal substrates to investigate the correlation between magnetic, structural and morphological properties of ultrathin films. Cu(100) and CU$_{3}$Au(100) single crystals were chosen as substrates to stabilize the high temperature fcc phases of Fe and Mn at room temperature. The magnetic properties were investigated by the Magneto-Optic Kerr-Effeet (MOKE). The structure of the films was characterized by Low Energy Electron Diffraction (LEED) and determined by quantitative, full dynamical analysis of LEED I/V spectra. LEED, Spot Profile Analyzing LEED (SPALEED), Medium Energy Electron Diffraction (MEED) and Auger Electron Spectroscopy (AES) were used to analyze the morphological properties. Films were deposited at 300 K (RT-films) or at 100 K followed by a subsequent annealing to 300 K (LT-films). In dependence on deposition temperature and thickness Fe grows in two different fcc and the bcc phase on the Cu(100) substrate. The ferromagnetic (FM) fcc Fe phase is stabilized on the Cu(100) substrate below about 4.5 monolayers (ML) independent of the deposition temperature. Within this coverage regime the magnetization is aligned perpendicular to the film surface. In correspondence to theoretic calculations the volumeof this phase (12.19 $\mathring{A}^{3}$) is expanded in comparison to the bcc (11.82 $\mathring{A}^{3}$) and the antiferromagnetic (AF) fcc phase (11.5 $\mathring{A}^{3}$). Every layer of the film is reconstructed perpendicular as weIl as parallel to the film surface. Atomic rows in fcc[011]-direction are sinusoidally sheared and corrugated in fcc [0$\overline{1}$1]-direction. This reconstruction is characteristic of a structural instability of the FM fcc Fe phase. Apart from the surfacelayer the reconstruction vanishes and the bulk interlayer distance decreases, when the thickness of RT-films exceeds 4.5 ML. The smaller atomic volume of the film bulk corresponds to the atomic volume of the AF fcc phase. Due to the reduced coordination number the FM fcc phase remains stabilized at the film surface. This causes a constant signal of the polar Kerr effect upon increasing thickness. Above 10 ML the fcc(100) Fe is transformed to bcc(110) Fe by a martensitic transformation. As a result of this transition the film is homogeneously magnetized parallel to the film surface. LT-films transform directly from the FM fcc(100) to the bcc(110) Fe phase above4.5 ML by an increase of the in-plane shear amplitude and the interlayer distance. Due to the reconstruction pattern of the FM fcc phase the bcc(110) domains are smaller than the domains of the RT-films. The structural transition causes a switching of the magnetization to in-plane. An increase of the in-plane lattice constant to 3.745 $\mathring{A}$ by deposition on CU$_{3}$Au (100) suppresses the formation of fcc Fe. Instead, Fe grows epitaxially strained in the bcc(100) structure up to 5.5 ML. Below this coverage a layer-by-layer like growth mode is found. The interface and the magneto-elastic anisotropy stabilize a perpendicular magnetizationdirection at low coverage. Fe and substrate atoms diffuse at the Fe substrate interface during deposition at 300 K This interdiffusion reduces the critical thickness for a reorientation of the magnetization to in-plane from 3.2 ML for LT-films to 2.3 ML for RT-films. Above 5.5 ML unstrained bcc(100) Fe is formed on the substrate uponincreasing coverage. Mn grows pseudomorphically on the CU$_{3}$Au(100) substrate up to 25 ML. Above a deposition temperature of 170 K layer-by-layer growth is found. Whereas the in-plane lattice spacing of the film remains unchanged upon increasing thickness, the interlayer distance changes up to about 11 ML. Above about 14 ML Mn is stabilized in the AF fcc modification, which is corroborated by a quantitative structural analysis at 16 ML. Due to an antiferromagnetic spin density wave with vector [100] the c/a-ratio is reduced by 5.2 %.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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